The invention relates to a process for fractionating phosphatide mixtures into two two or more fractions which are enriched in one or more of phosphatidyl choline (PC), phosphatidyl ethanolamine (PE), phosphatidyl inositol (PI) and phosphatidic acid (PA).
Phosphatides are commonly produced by water-degumming crude vegetable oils, particularly crude soy bean oil. In this process, water is finely dispersed in hot crude oil as a result of which most phosphatides present in the oil are hydrated and form a separate phase which is removed from the oil by centrifuge. The gums thus obtained are generally dried to yield lecithin, a product of commerce.
This lecithin is a complex mixture containing approximately 30% triglycerides and about 55% phosphatides, the remainder comprising sugars, glycolipids, partial glycerides, free fatty acids, residual meal particles and other compounds of an as yet unknown nature. The phosphatide composition of commercial soy lecithin can vary considerably but some of the variations reported in the literature (AOCS Monograph 12, Lecithins. Ed. B. V. Szuhaj and G. R. List, 1985, page 13) certainly stem from differences in analytical methods used. As an average composition, the following data can be quoted:
______________________________________ phosphatidyl choline (PC) 33% phosphatidyl ethanolamine (PE) 26% phosphatidyl inositol (PI) 23% phosphatidic acid (PA) 10% others, unknowns 8% ______________________________________
wherein the "others" also comprise lysocompounds such as lysophosphatidyl choline (LPC), etc.
Water-degummed oil still contains some residual phosphatides and according to U.S. Pat. No. 4,698,185 these can be removed from this oil by finely dispersing a non-toxic acid in the oil. After a contact time that is sufficiently long to ensure the decomposition of the alkaline earth salts of phosphatidic acid, a base is added to raise the pH above 2.5 without substantial formation of soaps whereupon the gums are removed and may be dried. Gums thus obtained contain both salts stemming from the acid and base used in the process and organic components which are predominantly triglycerides and phosphatides with a high PA-content.
Since lecithin has become commercially available, a number of processes have been developed to purify, modify, de-oil and fractionate this product, whereby the fractionation processes specifically aim at producing PC-enriched fractions. Such processes generally lead to products of enhanced functionality in the applications for which they have been developed.
One such de-oiling process has been described in British patent 412,224. It involves treating commercial lecithin with acetone or a mixture of acetone and alkanes. Since phosphatides are insoluble in acetone and triglycerides dissolve in this solvent, an oil-free lecithin with increased phosphatide content results.
A process aiming at PC-enrichment employing solvent fractionation of de-oiled lecithin is described in British patent 877,031. Alcohol is used as a solvent because this solvent exhibits a better solubility for PC than for PI, the solubility for PE being intermediate. According to German patent 14 94 952 the PC-selectivity of this process is improved by using aqueous alcohol and according to German Patent 16 92 568 further improvement is possible by adding monoglycerides. According to H. Pardun (Fette, Seifen, Anstrichmittel, 84, 1-11, 1982) it is possible to produce alcohol-soluble lecithin fractions with a PC/PE-ratio of more than 4 by first of all desugaring the gums, drying the desugared gums, de-oiling the dried gums and then fractionating the de-oiled lecithin. For the fractionating step the use of alcohol/hexane-mixtures is proposed. In a later article H. Pardun (Fette, Seifen, Anstrichmittel, 86, 55-62, 1984) provides a pretty comprehensive summary of the prior art including the fractionation techniques known from the afore-mentioned references.
In order to further enrich the PC-content of the PC-enriched fractions obtained by the alcoholic extraction of desugared, de-oiled lecithin, three types of process have been reported. The first type of process employs a chromatographic method (British patent 877,031) in that the PC-enriched alcoholic solution is treated with an adsorbent e.g. aluminum oxide which selectively adsorbs the PE present in the alcoholic solution. The second type of process (British patents 1 217 846 and 1 350 390) is based upon the conversion of the PE present in lecithin or its alcohol soluble fraction to acetylphosphatidylamine (APE) by treatment with e.g. acetic acid anhydride which APE is soluble in acetone at pH values above 8.5 or below 3.5 whereas PC is acetone insoluble. The third type of process (European patent 0 090 454) achieves a separation between PC and PE by treating a solution containing these two compounds with an alcoholic solution of e.g. magnesium sulphate as a result of which the PE preferentially precipitates.
The above processes have the disadvantage that they require a multitude of steps to arrive at just more or less pure PC and a PC-depleted residue and do not provide a route to fractions in which PA, PE or PI are the main constituent. Besides, the PC-yield attainable with the above processes is reputed to be unsatisfactory and to be 60% of theory at the most under favourable conditions.